This invention relates to a method and apparatus for forming a battery terminal bushing, and more particularly to an apparatus and method for forming a battery terminal bushing in which the porosity in the bushing has been substantially eliminated.
All conventional battery terminal bushings known to the Applicant are produced by die casting. Die cast battery terminal bushings are well known for the high degree of porosity within the cast material. It is virtually impossible to obtain a 100% porosity free bushing using the process of die casting. In die casting, molten metal is introduced into a mold cavity through a small opening or sprue, under high pressure. The high pressure causes a turbulence of the molten metal within the mold cavity. The molten metal is accordingly mixed with air, and when the metal solidifies, the air or gasses are trapped within the cast part.
Porosity in the cast material of a battery terminal bushing creates several problems. In a completed battery having a die cast terminal bushing, the sulfuric acid electrolyte within the battery casing tends to leak or creep through the pores of the bushing to the outside of the battery. The creepage of the electrolyte reduces the amount of electrolyte remaining in the battery cells. Moreover, the electrolyte which has creeped to the exterior of the terminals causes the terminals to corrode and thereby impairs the conductivity of the terminal connections. Moreover, the acid electrolyte exposed outside the battery is hazardous to the skin, clothing and other materials which contact the electrolyte.
The highly porous die cast terminal bushings conventionally used also permit the transmission of gas from the batteries while the battery is being charged. The electrolyte gasses are very explosive, and a faulty weld between the porous bushing and the element post can produce an electrical arc which would ignite the leaking gas.
Moreover, during the life of an electrolytic battery having die cast terminal bushings, both the liquid electrolyte creepage and the gaseous electrolyte leakage tend to increase over the life of the battery. The battery is subject to ordinary wear and tear, principally caused by vibration from the vehicle in which it is installed. Additionally, during the life of the battery, the plates tend to grow, that is they expand and, via the terminal conductive straps and element posts, can stress the element post/bushing weld. In the course of shipping and installation, the battery typically is subjected to rough treatment and mishandling as well as dropping or over-tightening the terminal connections. Consequently, the various seals in the battery deteriorate and become more susceptible to leaking.
The industry attempts to combat the electrolyte creepage and gas leakage problems of the porous die cast terminal bushings by improving the sealing between the battery terminal bushings, element posts, and the openings in the casing through which the post and bushings protrude. However, such attempts have not entirely overcome the problems of electrolyte liquid and gas leakage.
Examples of some attempts to overcome the problems involved in connecting and sealing battery terminal posts and bushings with battery casings are disclosed in the following U.S. patents:
______________________________________ 3,113,892 Albrecht Dec. 10, 1963 3,522,105 Sabatino July 28, 1970 3,767,467 Miller et al Oct. 23, 1973 4,143,215 Mocas Mar. 6, 1979 4,317,871 Wolf et al Mar. 2, 1982 4,645,725 Kump et al Feb. 24, 1987 ______________________________________
In all of the above patents, the battery terminal bushings are made in accordance with the conventional method of die casting.
One form of producing an electrical battery pole or bushing by a method other than die casting, is disclosed in the U.S. Scott U.S. Pat. No. 4,776,197, issued Oct. 11, 1988. In the Scott patent, a cold billet or cylinder of lead alloy is forced under pressure into a die in order to form the completed pole or terminal, and both opposite ends are sheared off to complete the trimming process. However, throughout the description of the process in the Scott patent, it is emphasized that the metal is not heated, and therefore never becomes molten, and in fact, the absence of heating the metal is considered an advantage in the Scott process.